[BUILD] 1176LN Rev D DIY

[RichardM]

Sorry that should be -10.93

 

[RichardM]

10.93!

 

[Echo North]

10.93!

You have that much DC there?  What is the AC?

 

[RichardM]

.07ac

 

[Echo North]

.07ac

You need to check your voltages, specifically in the signal amp.

http://mnats.net/files/1176REVD_VOLTS.pdf

 

[benlindell]

So I've now replaced the torodial transformer and redid the 2200uf caps, I'm getting a solid +28.5-30V but the -10 rail starts at -3.4ish and decreases slowly. What's going on here?

bump, just wondering if anyone has any ideas as to what might be causing the drop on my -10 rail?

 

[rockmonkey731]

Hey everyone, I posted this in a different thread but I figure this would be a better place.

Whenever I turn my rev D on, the fuse blows. I've upgraded to a 500mA slow-blo, and it still blows. I can't find any wires/solders touching, so i don't think it's a short issue. I need to test my components, and I'm wondering if I can test them while still in the pcb, or do I need to take out all the stuff I check?

Thanks.

EDIT: I turned it on and the fuse didn't blow, I know it's not calibrated, but the meter showed -infinity on GR, -10 on +8, and about -7 on +4. I turned the unit off, and C25 blew. It smoked and everything. It happened exactly when I turned the unit off, but the fuse never blew. I have no idea what could be going on, or what would make c25 blow when I turn off the unit.

 

[Harpo]

... I turned the unit off, and C25 blew. It smoked and everything. It happened exactly when I turned the unit off, but the fuse never blew.

Clean the board from electrolyte that came out of C25 (and be more specific whatever 'everything' else might be) and replace C25 and the probably blown diodes CR7 and CR8 (or double check polarity of CR7 and CR8 and if they are still diodes after C25 failed. These 1N400x can only take 1A and might have failed short). You fitted at least 50V rated caps for C25 and C26 with correct parts orientation ?

 

[rockmonkey731]

The seals at the top separated, and smoke/steam came out of the top for about a second. The polarity was correct, and it was the 2200uF 50v cap included in the mouser cart.

 

[benlindell]

Can someone with a working unit check out the voltages on the left side of CR7, CR8, CR9, CR10. I'm getting +32Vdc from CR7 and CR8. I'm getting -25Vdc from CR9 and CR10 but also 11Vac, are these normal?

 

[RichardM]

I have gone through and tested everything. I have found that my GR METER DRIVER section is all down about 2 vdc. I think the culprits might be r66, r72 and possibly r79. I am going to replace all of these when I get some new parts from mouser. Am I on the right track? Could low voltage in this area be the cause of no input in the unit? Thanks!

Rich

 

[rokus666]

By the way,

My second build was super easy and super fast. Thanks to all your help troubleshooting on the first one. Mnats' instructions are really idiot proof, you can't miss it if you attentively follow.

Great job once again, I have now two 1176 compressors. Time to move on to something else...

 

[Echo North]

Hey Ben,

I've got +40DC and +30DC w/ 8VAC.

Mike

Can someone with a working unit check out the voltages on the left side of CR7, CR8, CR9, CR10. I'm getting +32Vdc from CR7 and CR8. I'm getting -25Vdc from CR9 and CR10 but also 11Vac, are these normal?

 

[Echo North]

Could low voltage in this area be the cause of no input in the unit? Thanks!

No it shouldn't.

What is your DC at the Q11 gate?

 

[RichardM]

8.7 dc coming out of the side of Q11. This is where I first notice the big drop. -.04 and -.05 on either side of r65

 

[Echo North]

8.7 dc coming out of the side of Q11. This is where I first notice the big drop. -.04 and -.05 on either side of r65

8.7 VDC is your gate voltage?!?!

This should be a smaller - DCV.

 

[RichardM]

Sorry . I'm wrong. It is -.4 vdc when the red probe is on the g. Please forgive my ignorance but is this the correct location.

 

[Echo North]

Sorry . I'm wrong. It is -.4 vdc when the red probe is on the g. Please forgive my ignorance but is this the correct location.

Seems like it could be a little low.  Were you ever able to set your Qbias?

 

[RichardM]

I wasn't able to get the q bias set but I will try again. Is there anything special that I should do with all of the little trimmer pots before starting or is it only the Qbias trimmer that is in play for this? I did get the correct reading at the input xlr but no reading at the out put. By the way,thanks again for all of your help.

Rich

 

[Echo North]

I wasn't able to get the q bias set but I will try again. Is there anything special that I should do with all of the little trimmer pots before starting or is it only the Qbias trimmer that is in play for this? I did get the correct reading at the input xlr but no reading at the out put. By the way,thanks again for all of your help.

Rich

The voltages in the meter section on the voltage guide are dependent on the unit being calibrated correctly.

Right now if you can't pass audio, let's tackle that first.  Set you qbias to -2 VDC or more by placing your DC volt meter between the Q1 gate and ground.  Now turn your GR off by setting the attack to "off".  The should effectively disable all GR and Q1 turning your 1176 into a 2 stage mic pre with about 40 dB of gain.

If you're not getting any output like this, there is an issue in you preamp stages.  Feed a 1khz 1VAC signal into the input and set the in/out knobs to the middle.  Now let's see where the signal dies.

Measure the AC voltage at these points using GROUND as the reference.

1. Input XLR pin 2
2. + input at the PCB (by C1)
3. - of C7
4. Output XLR pin 2